US2766527A - Artificial tooth and process of making the same - Google Patents

Description

Och 1956 R. F. VINES ETAL ARTIFICIAL. TOOTH AND PROCESS OF MAKING THE SAME Filed Sept; 1, 1954 FIG-2 R w T m m RAYMOND F. VINES y CHARLES 01512 ATTOR United States Patent ARTIFICIAL room AND PRdeEss 0F Tim SAME Raymond F. Vines and Charles Die'tz York, Pa, assigno'rs to The Dentists" Supply Company of New York York, Pa., a- Corporation. of New York Application September 1, 1954, Serial. No. 453,595}

5 Claims. (CL

This invention relates to. artificial teeth and a process of making the same. More particularly, it re1at'es 'to.a process of making porcelain. artificial teeth and. the in;- verition pertains especially to the anchorage, means for retaining and afiixing pins to porcelain teeth. These anchorages are sometimes referred to in the artificial tooth field as tooth coils.

For many years it has been preferred to make dentures by securing artificial porcelain teeth tothe den base material, the teeth having anchoring pins w ch project from, the ridge lap surface or a surface i diately adjoining the same known as the pin shelf, The outer ends of the pin or pins which are afiixed to the teeth are headed and these headed ends of they pins be} come embedded within the denture base material so as securely to anchor, by mechanical means, the artificial teeth to the den-turebase material.

When the manufacture of artificial porcelain teeth having anchoring pins thereon was first undertake" may years. ago, the only metal suitable for forming said pins was. platinum, inasmuch as this was the only metal capable of withstanding the firing or fusing temperatures'of porcelain Without deterioration of oxidation of the metal While subjected to said temperatures. Platinum. was quite expensive at that time and, even though onl a small amount was required to form the pin or pins, for each tooth, such cost of platinum rather greatly increased. the cost of the teeth. As a result, especially about forty orfifty years ago, numerous eliorts were made to '0} vide tooth constructions which minimized the exist h'g platinum requirements of "artificial porcelain teeth.

From these activities came the current popular 15in construction in most artificial porcelain teeth, which is to use a small metallic anchorage of noble metal or alloy of such metals which is embedded in V of a porcelain tooth and is capable of withstand 'g the fusing temperatures of porcelain while the porc a n cuit or raw tooth containing the anchorage ifs be f 1 had or fused to produce a solid porcelain tooth A retaining or anchoring pin, formed from less exp metals than the noble metals, such as nickel, to Win 7 gold or an alloy of precious metals is. plated, the r is soldered to the anchorage within the interior of the porcelain tooth. The result of this is not only a much less expensive type of anchoring pin c'onstru'ction what was heretofore possible but a superior product.

When anchorages of this nature first were developed, they, like the entire anchoring pins used previously, were formed from platinum or alloys consisting largelyof platinum. About the time of the first World War, platinum became e'xc ee'dinglyscarce and increased considerably in price. As a result", a search for acceptable substitutes for platinum resulted in a number of alloys being developed. One of these which still is wide use consists of 65% gold and 35 palladium. Itwas found this alloy withstands the" fusingternpera tu re of porcelain which is somewhere in the vicinity of 220(1); f0

2400 F., and the same does not visibly oxidize, therelay 2,766,527 hatented Oct. 16, 1956 2 forming; asuitable surface to which an anchoring pin may be soldered when said "alloy is used as an anchorage which embedded within the porcelain tooth.

when the revaluation of gold occurred about twenty years ago, the increase in the cost of gold made the use thereof for tooth anchorages less d sirable. As a con sequence efforts were made to develop suitable lower gold content alloys. Since that time a number of other alioys' have been developed and. have been widely used such as for example the alloys. within'the' range of the Die Z Patent No. 2,310,732, dated February 9', 1943, and particularly Within the range 60 to palladium, 2 to 10% silver and the balance gold and/or plati- These alloys, lilielthel 65%. gold, 35% palladium and the 50% gold, 5.0%v palladium alloys, when used as, anchorages in normal tooth firing procedures do not develop a visible coating of palladium oidde and hence insofar" as the artificial tooth field isl oncerrfid are nonoXidizifig' alloys. The cost aid density of palladium as compared to gold is highly favorable to the use. of pall'adiur'n and hence the high palladium content alloys referred. to, above provedsatisfactory from the cost stand- Paint.

Obviously the cost of the alloys used for anchorages is an important consideration in the cost of artificial e h. A cording y fl ua ons in the pt e of the component metals; particularly plan an, palladium and gold re e t d ifr'i, 'changestn, and. c mpo .i'tic ns. wi hin. t ranges s il a t" Fo xf lil he. 70%,n 11la n Y I 1 1 55 111 3? W a. dfifihblt 3C 0!- age, alloy when platinin'n was selling at $37.00 per troy ounce but. with the present price of platinum about $90.00 per troy ounce thisalloy' is not used. 7

r The use of substantially pure Palladium is desirable from the standpoint or cost, especially based upon current market price of platinum, gold, palladium and silver which prices respectively per ounce, are approximately 3990,00, $35.00, $22.50, and $1.0m, Thefollowing table gives a comparison of the costs of the four alloys referred to above with substantially pure palladilir n.

Alloy Percent-bywelght l rm ozt Unit Pit ndnim Density Cost, Volume QQstNQted, G /caq l rs 20 rcen :Au 'Pd Pt Ag Dollars Less 65 i 35 16174' area 51.25 47 50 50 15.65 28.75 4 4.99v to; 33 6d 3 14.36 25.98 37.30 27 70' 25 5 14.27. 38130 54. 65 51 .c 12:00. 22.50 27.00 Although the use of palladium" for tooth anchorages is desirable from the cost standpoint, it has been known for many yearsthat palladium, when subjected to" ternper'atur'es at which porcelain vi-t'rifi'es', will on cooling oiridize to produce a bluish black layer or coating of pall adiuni oxide on the interiors of cup-like anchorages for example. Further, the gas sorb'i'ng' tendencies of pal- Indians are well known. It can be surmised that probably because :of the above described properties of palladiuni that interested parties the artificial tooth field rejected without trial the use of palladium in substantially pure state for tooth anchorages; on the theory perhaps that palladium oxide would interfere with necessary soldering operation to connect the pin to the anchorage and the gas sorbing tendencies oi palladium probably were presumed to create bubbles to such an extent between the outer surfaces of the anchorage and the adjacent porcelain particles fused thereto tl 'iat a firm bond would not, be emitted between the anchorage and the porcelain.

In accordance with the present invention, it now has been discovered that pin anchorages may be made from substantially pure palladium or from alloys containing relatively high percentages thereof, so that they constitute essentially palladium, if the metal is processed annealed in a suitable atomsphere or under otherwise controlled conditions so as to avoid or minimize contamination of the palladium or high content palladium alloy with deleterious gases such as would produce bubbles between the porcelain and the anchorage if the palladium is not so treated. This feature of the invention is regarded as important inasmuch as it now makes possible the use of substantially pure or high palladium content palladium anchorages which are not resistant to oxidizing and to which porcelain may firmly be fused without the formation of any appreciable quantity of gas bubbles.

Another important feature of the present invention constitutes the discovery that the palladium oxide which will form on the interior, for example, of cup-like anchorages when embedded within porcelain tooth biscuits and vitrified or fused to render the porcelain solid will not interfere with the silver soldering operation required to attach the pin to the anchorage.

After the tooth with the anchorage embedded therein is vitrified and cooled, the interior of the anchorage or otherwise exposed surfaces therein will become oxidized or covered with a thin bluish black coating of palladium oxide. When the pin is silver soldered to the anchorage in the tooth at a temperature of about 1450 F. in the presence of a flux, both the high temperature and the low oxygen pressure on the fluxed anchorage lead to disassociation of the palladium oxide with the result that a firm union between the pin and anchorage is formed. The subjecting of the anchorage to said temperature of about 1450 F under the conditions of fluxing automatically decomposes any layer or coating of palladium oxide formed thereon and thus a clean surface is provided on the palladium anchorage to which silver solder attaches itself and connects the anchoring pin thereto upon cooling to normal temperatures. In this process the original surface of the anchorage, which was initially oxidized, is

dissolved in the silver solder forming an alloy bond.

Details of teeth including anchorages and having anchoring pins attached thereto in accordance with the foregoing advantageous features of the invention are described in the following specification and illustrated in the accompanying drawing forming a part thereof.

In the drawing:

Fig. 1 is a vertical sectional elevation of an exemplary anterior tooth, taken on a plane extending labial-lingually and showing an anchorage embedded within a porcelain tooth and a pin soldered thereto.

Fig. 2 is an enlarged fragmentary sectional view on a plane similar to that used in Fig. l and illustrating on a larger scale an exemplary tooth coil or anchorage positioned on a mold post as it appears during the process of investing said anchorage in raw porcelain dough during the molding of an artificial porcelain tooth.

Fig. 3 is a view similar to Fig. 2 but showing the mold post removed and illustrating the relative position of the anchorage in the porcelain tooth after the porcelain has been vitrified, this view also illustrating in heavy lines a layer of palladium oxide appearing on the interior of the anchorage.

Fig. 4 is a sectional fragmentary view similar to Figs. 2 and 3 but illustrating a pin soldered to the anchorage as it will occur in a finished artificial porcelain tooth.

Porcelain artificial teeth, such as the one indicated and illustrated in vertical longitudinal section in Fig. 1, are formed in suitable molds which incidentally are provided with means to facilitate the placing of an anchorage 12 within the tooth. Various types of molds are suitable for this purpose, one well known type being illustrated in U. 5. Patent No. 1,547,643 to CI PP, dated July 28, 1925. The molds usually comprise at least two separable 4 mold parts which cooperate to define a suitable cavity within which a tooth 10 is molded.

One of the mold components usually is provided with a post 14, a portion of which is shown in Fig. 2 of the drawing. It will be noted that the anchorage 12, which is metallic and, in the exemplary illustration herein, is cup-shaped, is slidably and removably fitted on the free end of post 14 which projects from one of the mold sec tions or members, not shown, whereby the anchorage 12 is supported within the mold cavity by the post 14. A quantity of raw tooth dough, which has a putty-like con sistency and includes porcelain components such as pulverized feldspar and organic binding agents, is introduced into the mold cavity and surrounds the anchorage 12 on the end of the post 14. The raw tooth dough is forced into firm engagement with the outer surfaces of anchorage 12 and the molded raw tooth while still in the mold parts, usually is baked while it remains in these parts for a period of time and at a sufficient temperature, of about 500 or 600 F. to remove the moisture from the molded raw tooth and render it sufficiently hard that it might be handled without danger of fracture or being mis-shapened.

After such preliminary baking, which is not accomplished at sufliciently high a temperature as to fuse the porcelain components, the raw molded tooth or biscuit. as it is known in the artificial tooth field, is placed on a suitable holder resistant to high temperatures and then transferred to a firing furnace where the raw biscuit is fused so as first to burn off the binding material, if used, and then unite the porcelain particles to each other so as to render the tooth 10 substantially homogeneous and solid. Such fusing of the porcelain particles also causes the tooth 10 to be fused to the anchorage 12. It also will be noted from the various figures that the exemplary anchorage is provided with an annular flange 16 which fixedly positions the anchorage within the body interior of the tooth 10.

When the anchorage 12 is formed either from substantially pure palladium or from an alloy which is relatively high in palladium, such as set forth in detail hereinafter. the interior of the anchorage 12 will be oxidized after being elevated to porcelain fusing temperatures, of the order of 2250 or 2300 F., and then being cooled to room temperature for example. When the vitrified or fused tooth containing the anchorage 12 is cooled to room temperature, it will be found that the interior of the an chorage is coated with a layer 18 of bluish-black palladi um oxide. This is due to the fact that the interior of the anchorage 12 is exposed to the fusing atmosphere in view of the opening 20 which is formed in the tooth 10 when the pin 14 is separated from the molded tooth, the opening 20 also receiving the anchoring pin 22.

Presumably, it has been supposed heretofore that the existence of such a layer of palladium oxide on the interior of an anchorage in a tooth would preclude the obtaining of a firm union by solder, for example, between such anchorage and a pin it anyone attempted to solder a pin to said anchorage. Further, the bluishblack color of the oxide may have given an impression that it would darken a tooth and render it undesirable for use. In any event, to the knowledge of any parties acquainted with the instant development, neither substantially pure palladium or an oxidizable alloy having a high palladium content has been used heretofore as a tooth anchorage.

In accordance with the present invention, it now has been discovered that, when a pin such as exemplary pin 22, which for example may be formed from nickel and has a plating of gold or gold alloy thereon, is soldered by silver solder 24 to the cup-shaped anchorage 12, the high temperature, about 1450" F. and the fluxing necessarily employed to prevent oxidation of the silver solder, reduces or decomposes the palladium oxide, thereby effecting a firm bond between the anchorage 12 and pin 22. It 1185 been found that the soldered joint is a very strong one ..in,the assembly and when.v the. assembly is. tested to destruction either the porcelain tooth or pm, but not the solder joint, will fail. Upon sectioning soldered pins and anchorages within porcelain teeth following such soldering operations, it has been found that the solder joint is in every observable respect equivalent to the joints formed with the so-called non-oxidizable anchorage compositions. i i Q In view of the fact that the raw materialfrom which the tooth is formed closely conforms to'the anchorage 12 while the tooth is being molded, when the molded tooth biscuit is subjected to fusing temperatures, the fact that the outer surface of the anchorage 12 is closely covered by the raw porcelain material results in said outer surface of the anchorage 12 being protected from oxidation while the anchorage is cooling from the fusing temperatures. Thus, although the interior of the an chorage 12 will become oxidized under such conditions, the outer surface of the anchorage will remain bright and the union between the fused porcelain material and anchorage will be firm and solid and not impaired by the formation of any palladium oxide, thus in no way impairing the color of the tooth.

Either substantially pure palladium or high palladium content alloys are preferred to form anchorages in accordance with the present invention, one reason being the economic factor of price as compared with other noble metals, it being understood that usually only noble metals are satisfactory for such purposes. However, another factor favoring the use of this type of anchorage is the fact that palladium is more compatable with feldspathic porcelain, in that it has a coefiicientof expansion nearer that of porcelain than the high gold alloys. If desired to render the anchorage harder, thanthat" afforded by substantially pure palladium, suitable small quantities of noble metals such as silver, gold, platinunniridium, rhodium and ruthenium, or alloys thereof, might be alloyed with the palladium. Alloys which have been found desirable and operable in accordance with the present invention, in addition to using substantially pure palladium, are set forth in the following table:

In the foregoing examples, all percentages are given by weight.

Possibly another deterent to the use of palladium as an anchorage in artificial porcelain teeth has been the well known knowledge that palladium is subject to gases being dissolved or sorbed therein. When ordinarily processed palladium or high palladium content alloys are used for anchorages, the gases dissolved or sorbed therein, especially at porcelain fusing temperatures, tend to evolve from the anchorage and form bubbles between the anchorage and the porcelain material adjacent the same. It readily is understandable that, if a substantial number of bubbles occur around the exterior of an anchorage, said anchorage may become loosened from the tooth so that, when a pin is soldered thereto the tooth and pin will tend to move relative to each other. Such a situation readily could result in a tooth becoming loose relative to a denture in which it has been processed.

Now it has been discovered that if palladium or high palladium content alloys such as are usable in the present invention are process-annealed in certain atmospheres the tendency of the anchorages to dissipate gas bubbles while the raw teeth are being fused is either prevented or greatly minimized. One suitable atmosphere comprisessteam; others are hydrogen or nitrogen containing small amounts of hydrogen so as to be certain of rendering ineffective any oxygen which might be present in ordinary nitrogen. Still othersuitable atmospheresare the noble'gases such as argon and helium, and vacuo.

The purpose of the atmosphere is to prevent damage to the palladium during the annealing treatment which is necessary inprocessing a cast ing-0t to the thin. strip used as stock for anchorages. Normally in the artificial tooth industry, metal or alloy stock used for tooth anchorages are process-annealed to permit reduction of the cast ingot to wire strips or sheets used to form an chorages. Annealing normally is not performed on the finally shaped anchorages which are used in teeth. The process-annealing times and temperatures are of course dependentupon the size, shape and form of the -palladium at'the time of annealing, the amount of prior cold work and the exact manner ofannealing. It has been found that, particularly when the palladium is re duced to the smaller diameter wires or strips, strand annealing is preferable to annealing in coil. Whatever the conditions of annealing, the temperature and time of annealing must be accordingly adjusted so that the palladium is softened and the work hardening is removed to -permit additional working. In addition, the atmosphere surrounding the palladium must prevent oxidation or carbonization of the metal. The preferred atmos pheres are steam, hydrogen or nitrogen with up to 7% hydrogen. Other atmospheres which will likewise protect the palladium are also considered within the scope of the invention.

Less suitable but usable anchorages of palladium have been produced by annealing in air at the lowest possible temperatures, about 1000 F. for severely worked pal: ladium, followed by quenching in dilute formic acid or alcohol to reduce the surface oxide formed during such annealing. w

Althoughthe invention is based upon discovery and practical use of the procedures set forth, it is believed that the reason for the observed effects are as follows. It has long been known in the precious metal field that the surface of palladium is seriously damaged'with intergranular separations and sometimes blistering if it is alternately annealed in an oxidizing and reducing atmosphere. Atkinson and Gladis report on this type of damage in Transactions of American Institute of Mining and Metallurgical Engineers, Institute of Metals Division, volume 166, 1946, page 426, in a paper entitled A study of the behavior of ruthenio palladium in torch flames with the object of improving soldering technique.

It is believed that this surface damage is due to the interaction of oxidizing and reducing gases within the metal. For example if palladium is first annealed in air some oxygen enters and diffuses into the palladium to a depth depending upon the time and temperature of an nealing. This oxygen is dissolved in the metal and is not dependent upon the formation of palladium oxide which will not form at temperatures above about 1450 F. in air. If such air annealed palladium is now reannealed or reheated in a hydrogen atmosphere, hydrogen which diffuses faster than oxygen, will diffuse into the oxygen containing. palladium and react internally with the oxygen present to form steam. Since steam cannot diffuse out of the solid palladium it, under the influence of the high pressures generated because of the high temperatures, will open up grain boundaries to escape or form blisters. This reaction produces a roughened or matte surface with a greatly increased surface area as compared to the original undamaged surface and, in addition, the palladium frequently has numerous sub-surface voids. The opposite change from an initial hydrogen atmosphere to a final oxidizing atmosphere produces a much less severe surface damage or no damage at all. This difference in behayior, depending upon whether hydrogen or oxygen (air) is the initial atmosphere, is thought to be due to differences in the rate of diffusion of these gases in the metal. Y

In the ordinary method of manufacturing artificial teeth an initial reducing atmosphere is automatically and necessarily developed within the tooth and adjacent to' the anchorage during firing by the burning off of the organic binder. This reducing atmosphere is normally dissipated at the completion of the burning-off stage and the beginning of the oxidizing stage at a temperature of about 1800 F. For the balance of the tooth firing operation the tooth and anchorage are in an oxidizing atmosphere but the oxygen pressure on the surfaces of the anchorage in contact with the porcelain is dependent upon the equilibrium oxygen pressure of the porcelain which acts in the nature of a fiux preventing oxidation of the anchorage.

Thus, tooth manufacturing normally entails a change of atmosphere insofar as the anchorage is concerned but the change is from an initial reducing atmosphere to a final oxidizing atmosphere and such atmosphere changes are known to produce a much less severe surface damage than the change from an oxidizing atmosphere to a redu'cing atmosphere. The previous statement of course presumes that the anchorage has not been previously exposed to an oxidizing atmosphere. Such a presumption has, until the instant invention, not been justified for either pure palladium or the common anchorage alloys which are usually annealed in air or in gas furnace atmospheres containing a substantial amount of oxygen.

Therefore, when the palladium, as has been usual for the precious or noble metals and alloys, is process-annealed in air or high oxygen content atmospheres and formed into an anchorage, then serious surface damage 'with the possible development of sub-surface voids is likely to occur during the initial reducing atmosphere firing necessarily encountered during the manufacture of teeth. Exactly how or why these reactions produce the bubbles in the porcelain adjacent to the anchorage is not known. It may be that the greater activity of the anchorage surface, caused by the increased surface area produced by the roughening developed during surface damage, encour ages greater carbonization during the burn oif period which carbonization and subsequent oxidation, late in the firing cycle, causes the bubbles in the porcelain. Althoughthe exact cause of the bubbles is not known, it is known that anchorages made from palladium which is first process-annealed in air or gas furnace atmosphere produces bubbles in the porcelain around the anchorage while, when the palladium is processed in steam, hydrogen, or one of the other atmospheres set forth above, the porcelain adjacent the anchorage is substantially free from bubbles.

The suitability of palladium annealed in air at low temperatures and quenched in formic acid or alcohol is thought to be due to the lesser amount of oxygen dissolved in the palladium at these lower temperatures. Likewise, the suitability of the higher gold and platinum alloys is thought to be due to the lesser amount of oxygen dissolved in these alloys even when annealed at higher temperatures in air.

When the palladium has been annealed by any of the processes set forth above, it has been found that substantially n'o bubbles are formed around tooth anchorages made therefrom when the tooth incorporating the anchorage is subjected to porcelain fusing temperatures. As a result, the porcelain is fused in close union with the outer surface of the anchorage. Further, the palladium coils formed from stock first process-annealed in accordance with this invention are exceptionally bright where protected by the porcelain tooth material, thus minimizing any tendency of such coils to discolor or otherwise mar the appearance of the finished porcelain tooth.

Many alloys containing palladium have been developed heretofore due to the fact that the price and lower density have made the use of palladium desirable. However, in all instances known where palladium alloys have been used as tooth anchorages as the one for example, in said U-. S; Patent No. 2,310,732 to Dietz, an alloy has been 8 developed which, when subjected to porcelain fusing tethp'eratures would not oxidize visibly upon being cooled below said temperatures. However, expensive nobleinetals are required in such alloys to render them non-oxidizable, thus defeating the purpose of the present invention.

From the foregoing, it will be seen that the present invention provides the first practical use of substantially pure palladium or an alloy which essentially comprises palladium in the amount of atleast substantially 86%, for tooth anchorages in porcelain artificial teeth and regardless of whether such anchorages oxidize in areas u'nprotected by the porcelain. In adapting this material to use as tooth anchorages, it has been necessary to overcome several outstanding difiiculties, principal among which are the eliminating or minimizing the tendency to pro= duce gas bubbles between the anchorage and the porcelain material of the tooth, and the effecting of a metal to metal soldered connection between the pin and anchorage, as distinguished from a soldered connection to an oxide coating on the interior of the anchorage. The present invention successfully has overcome these ditficulties and a tooth having a relatively inexpensive anchorage, as compared to anchorages made of other more expensive noble metals or alloys of noble metals which have been used heretofore.

In adapting palladium to use as tooth anchorages in accordance with the present invention, an anchorage is afforded which is much less expensive and has a coefficient of expansion more compatable with porcelain than materials heretofore used for anchorages, with the result that a decrease of cracking in the porcelain around the anchorage results as compared with anchorages previously used. The anchorages proposed by the present invention also minimize the possibility of melting of the anchorage during the fusingof the porcelain teeth and soldering as compared with prior experiences with lower melting point conventional anchorages. Further, anchorages made in accordance with the present invention compare most favorably with any previously used anchorages in strength tests.

While the invention has been shown and illustrated in its several preferred embodiments, and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried out in other ways falling within the scope of the invention as claimed.

We claim:

1. An artificial tooth comprising a porcelain body having an anchorage therein comprising from 86 to palladium, said tooth being fused to said anchorage, and a pin soldered to said anchorage to secure said pin to said tooth, said anchorage being characterized by being substantially free from palladium oxide.

2. An anchorage for an artificial porcelain tooth comprising between 86% and 100% palladium and processannealed in a manner to render the same substantially free from gas contamination, said anchorage being char acterized by porcelain being fusible thereto with substantially no formation of gas bubbles adjacent said anchorage at temperatures to which it is subjected while said porcelain is being fused thereto and capable of being soldered to a tooth pin according to usual procedure.

3. An artificial porcelain tooth having an anchorage fixed therein, said anchorage consisting of substantially pure palladium, and a pin soldered at its inner end to said anchorage and projecting from said tooth at its other end, said anchorage being substantially free from palladium oxide and the porcelain of said tooth being fused thereto.

4. The process of forming an artificial pin-type porcelain tooth comprising the steps of process-annealing an anchorage comprising essentially palladium in a gaseous atmosphere suitable to minimize contamination thereof by gas, investing said anchorage in raw porcelain dough, molding the same into a raw tooth having an opening extending therethrough to said anchorage, vitrifying said raw tooth to fuse it to said anchorage and unite the raw porcelain particles into a homogeneous mass, said porcelain shielding the outer surfaces of the anchorage from contact by the atmosphere in which said tooth is vitrified while the interior thereof is exposed to said atmosphere, placing a pin and fluxed solder within said opening and in contact with the interior of said anchorage, subjecting said tooth and pin to a temperature of about 1450 F. to melt said solder and decompose any palladium oxide within said anchorage, and cooling said tooth and pin to solidify said solder, thereby to permanently unite said pin and tooth.

5. The process of forming an artificial pin-type porcelain tooth comprising the steps of process-annealing a palladium anchorage comprising essentially palladium in a gaseous atmosphere suitable to minimize contamination thereof by gas, investing said anchorage in raw porcelain dough, molding the same into a raw tooth having an opening extending therethrough to said anchorage, vitn'fying said raw tooth to fuse it to said anchorage and unite the raw porcelain particles into a homogeneous mass, utilizing said porcelain to shield the surfaces of the anchorage in contact therewith from contact by the atmosphere in which said tooth is vitrified while the interior thereof is exposed to said atmosphere, placing a pin and fiuxed silver solder within said opening and in contact with the exposed surfaces of said anchorage, subjecting said tooth and pin to a temperature of at least 1450" F. to melt said solder and decompose any palladium oxide on said an chorage, utilizing the melted solder to cover and prevent oxidation of said previously exposed surfaces of said anchorage and cooling said tooth and pin to solidify said solder, thereby to permanently unite said pin and tooth.

References Cited in the file of this patent UNITED STATES PATENTS 1,019,233 Edwards Mar. 5, 1912 2,169,731 Lease Aug. 15, 1939 2,310,732 Dietz Feb. 9, 1943

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